1. Field of the Invention
The present invention relates to an information storage device for storing information and a write control circuit for controlling writing of information to an information recording medium.
2. Description of the Related Art
There is an ever-increasing amount of information in conjunction with development of information society, where development of a large-capacity and low-cost storage device is required to address this increasing amount of information. In particular, a magnetic disk for performing information access in magnetic fields is receiving attention as an information-rewritable high-density storage medium. For the sake of furthering the large capacity, active research and development are going on as to a magnetic disk device having the magnetic disk and a head built therein to perform information access to the magnetic disk with the head.
FIG. 1 is a conceptual diagram of the magnetic disk device.
The magnetic disk device normally has multiple magnetic disks 10 placed concentrically therein, and a head 20 for applying the magnetic fields is provided on each of the two sides of each individual magnetic disk 10. The magnetic disk 10 has linear tracks 12 provided thereon, and the tracks 12 provided at the same location on the multiple magnetic disks 10 are collectively handled as a cylinder 11. The magnetic disk 10 is divided into multiple areas (sectors 13) in a circumferential direction of the tracks 12, and the magnetic disk device has a series of logical addresses assigned to each of the sectors 13.
The magnetic disk device is often built in or connected to a host device, such as a personal computer. If a logical address is specified by the host device, the magnetic disk device calculates a physical address configured by a cylinder number representing one of the multiple tracks 12, a head number representing one of the multiple heads 20 and a sector number representing one of the multiple sectors 13 based on the specified logical address so as to move a scanning position 14 of the head 20 to the sector 13 indicated by the calculated physical address. The magnetic disk 10 is rotated in a state of having the head 20 moved so as to perform information access along the track 12 to the sector 13 to which the logical address specified by the host device is assigned.
Japanese Patent Laid-Open No. 52-040111 describes a technique of recording the physical address in each of multiple storage areas (the sectors) on the magnetic disk in advance, and when writing information to the storage area indicated by the physical address calculated based on the logical address, moving the head to the storage area indicated by the calculated physical address and writing the information after confirming a match between the physical address recorded in the storage area of a location to which the head is moved and the calculated physical address. According to the technique described in Japanese Patent Laid-Open No. 52-040111, it is possible to write the information securely at the location indicated by the calculated physical address and reduce problems of writing the information to a wrong location.
In recent years, there are an increasing number of failures of hardware, and in particular, those of RAMs due to higher integration of semiconductors. There is also a problem of a failure as to the magnetic disk device, for instance, that the RAMs are used in a circuit for calculating the above-mentioned physical address and so the information is mistakenly written to a sector different from the sector to which the specified logical address is assigned due to a failure of the RAM.
In the case where the logical address is converted to a wrong physical address according to the technique described in Japanese Patent Laid-Open No. 52-040111, however, the head is moved to the sector indicated by that wrong physical address so as to have the information written to a wrong sector in the end. In the sector having the information thus mistakenly written thereto, it is no longer possible to read out that information. In the sector having the specified logical address assigned and no information written thereto, there is also a problem that wrong information recorded therein by chance is read and data gets garbled.
The above-mentioned problem is not limited to the magnetic disk device but is the problem that generally arises in a field for using an information storage device which calculates a location on an information recording medium based on the logical address.